1. Field of the Invention
The present invention relates to an engine balancing system using reciprocating balance masses which are driven directly by cam lobes integrated with the engine""s crankshaft. The balance masses are resiliently mounted to the engine""s cylinder block under the crankshaft.
2. Disclosure Information
Engine designers have used a veritable plethora of mechanisms and systems to reduce the dynamic unbalance of engines. Such designs have used reciprocating masses such as that shown in U.S. Pat. No. 4,688,528. Another well known method for balancing engines involves the use of rotating balancers. Such balancers suffer from the problem that they do not address the first and second order unbalances in a single assembly. Also, balance shafts typically take a large amount of space are not energy efficient because of the frictional losses associated with them. U.S. Pat. No. 4,781,156, which is assigned to the assignee of the present invention, discloses a crank driven balancing mechanism which is applied at a single location in an engine and which cannot, therefore, address the pitching couple of an engine.
As used herein, the term xe2x80x98pitching couplexe2x80x99 means the tendency of an engine to rotate or, more precisely, rotationally oscillate in a vertical plane aligned along the longitudinal axis of the engine. Inline engines, particularly I4 and I5 engines, can have vertical shaking forces or pitching couples which are due to the accelerations of the pistons and the valvetrain. Inline 5 cylinder engines have been built with balance shafts to cancel either the first order or the second order pitching couples but not both at the same time. In an inline engine, all unbalance caused by piston accelerations is in a vertical plane, resulting in the previously mentioned vertical shake and/or pitching couples. Also, most of the unbalance caused by the accelerations of the valvetrain is also in a vertical plane, resulting in vertical shake or pitching couples. The inventor of the present invention has determined that the use of two reciprocating balancers located near the front and rear regions of the engine will cancel all of the vertical unbalance caused by the piston accelerations and all of the integral order vertical unbalance generated by the valvetrain accelerations. If both of the balancers were to move up and down in phase, they would generate vertical shake. However, when the balancers move up and down out of phase with each other, they generate a pitching couple which counteracts the pitching couples produced by the valvetrain and pistons of the engine. Because the motion of each reciprocating balancer is determined by cam contours which are ground onto the crankshaft cheeks, the contour can be ground to address any and all orders of vibration that are integral numbers greater than or equal to 1.
A reciprocating internal combustion engine includes a cylinder block and a crankshaft housed within a cylinder block, with the crankshaft being journaled to the cylinder block by a plurality of main bearings. The crankshaft has a first end and a second end, several crankpins, and cheeks that connect each crankpin to adjacent main bearing journals. A plurality of balancers including reciprocating balance masses is located in the engine, with one of the balancers being attached to the cylinder block near the first and second ends of the crankshaft. Each of the balancers includes a plurality of cam lobes formed on the cheeks of the crankshaft and a reciprocating balancing mass resiliently mounted to the cylinder block below one of the main bearings. The reciprocating balancing masses are preferably spring mounted and they are urged into contact with the cam lobes which are formed on the cheeks of the crankshaft. A plurality of cam followers is in operative contact with the balancing masses and the plurality of cam lobes. At least one of the cam followers is engaged with at least one of each of the cam lobes. Each of the cam followers is operatively connected with one of the reciprocating balancing masses such that the balancing masses will be caused to reciprocate along a generally vertical axis in response to the rotation of the crankshaft and its integral cam lobes.
In a preferred embodiment, two reciprocating balancers operate on an engine, with one of the balancers near the front end of the engine and one near the rear. These two balancers can effectively cancel all integral order inherent unbalance of the engine that is located in the vertical plane of the engine. The motion of each balancer is determined by the contour of the cam surfaces formed on the crankshaftxe2x80x2xe2x80x3 cheeks. This motion of each balancer is repeated for each rotation of the crankshaft, but the contour of the cam may be formed to produce motion that is a combination of first, second, and other integral orders of crankshaft rotation. When both balancers are accelerated in the same direction, the reaction against the enginexe2x80x2xe2x80x3 structure is a force. When the two balancers are accelerated in opposite directions, the net reaction against the enginexe2x80x2xe2x80x3 structure is a couple. If desired, the cams may be contoured such that the balancer masses have a motion that is a composite of various integral orders, both in phase and out of phase with each other, so that forces and couples of all integral orders are cancelled.
According to another aspect of the present invention, a method for balancing the couples generated by the piston acceleration forces of an inline five cylinder reciprocating internal combustion engine having a cylinder block and crankshaft include the steps of providing a plurality of cam lobes upon the crankshaft, with the cam lobes being integrated with cheeks formed on the crankshaft, and providing a plurality of balancing masses which are resiliently mounted to the cylinder block at both ends of the crankshaft. Finally, the present method includes reciprocating the balancing masses with a plurality of cam followers driven by the cam lobes and operatively connected with the balancing masses, with the cam lobes being indexed such that the balancing masses are reciprocated with 180 crankshaft degrees of phase separation.
It is an advantage of the present invention that the present balancing system acts to effectively mitigate engine vibration without increasing to any great extent the package volume of the engine.
It is another advantage of the present invention that the present vibration damping system may be implemented in an engine at a lower cost than known vibration control systems.
It is yet another advantage of the present invention that the present vibration damping system does not rely on any type of chain drive and utilizes lightweight construction.
It is an advantage of the present invention that the present vibration balancing system may be utilized with either inline or v-block engines having various numbers of cylinders.
Other advantages, as well as features and objects of the present invention, will become apparent to the reader of this specification.